KR20020035170A - A method and arrangement for timing the diversity weight changes in a cellular radio system - Google Patents

Abstract

A method and apparatus are provided for timing the change in diversity weights in a wireless connection between a base station and a terminal. The response timing mode is selected from a plurality of predetermined response timing modes. The terminal informs the selected response timing mode. An initiation is received from the terminal, and the terminal is responded to the initiation by changing a predetermined diversity weight such that the exact moment affecting the change is determined by the selected response timing mode.

Description

Method and arrangement for timing the diversity weight changes in a cellular radio system

In a cellular wireless system, spatial diversity means that a communication connection between a mobile terminal and a base transceiver station or BTS proceeds simultaneously through at least two antennas in the BTS. In order to take full advantage of spatial diversity in the downlink direction, the relative transmit power and phase directed through the other antennas must be carefully balanced. The relative transmit power level and phase of the other antennas may be represented by some composite weights determined by the control unit inside the BTS or other fixed portions of the network.

A number of downlink diversity schemes have been proposed in the standard to define WCDMA or wideband code division multiple access portions of the proposed third generation digital cellular communication system. Setting up a so-called closed-loop TX diversity scheme, i.e., a mobile terminal or user equipment (UE) sends this feedback information in the uplink direction and adjusts the antenna weight to UTRAN or UMTS global radio connections. It is known to use in a network (where UMTS comes from a general purpose mobile communication system). Communication errors may cause the feedback loop to not function properly, which in turn may cause the UTRAN to put another antenna weight in use other than the UE actually requested. To recover the error condition, the UE can optionally use verification of the so-called antenna weight. The purpose of the verification is to check whether the appropriate antenna weight is in use at a particular base station.

Validation algorithms are known as above and are not within the scope of this patent application. However, in order to properly operate known verification methods, the UE must know exactly when the BTS changes the antenna weight. Suggestions known at the priority date of this patent application suggest that every change in downlink transmission power (within antenna weight) is a known part of the frame because the downlink transmission consists of a continuous period of frames and a predetermined time structure. Suggest that they occur at some time in relation to the field. In particular, it has been proposed that the change in downlink transmission power should always be influenced at the beginning of the pilot field since all downlink frames contain a predetermined pilot field. It is taken for granted that this means the beginning of the next pilot field which will be transmitted alternately after that moment when the feedback information is received at the UTRAN.

1 illustrates certain timing considerations in connection with the known apparatus described above. Line 101 is a train of downlink transmission slots as the slots appear in the base station, and line 102 is the same train of downlink transmission slots as the slots appear in the UE. Line 103 is a train of uplink transmission slots as slots appear in the UE, and line 104 is an identical train of uplink transmission slots as slots appear in the base station. The finite propagation speed of the radio wave results in a propagation delay (D): The receiving station shows the same train of transmission slots up to a later delay (D) than the transmitting station. The time relationship between the uplink and downlink slot boundaries is fixed to achieve some synchronization.

Each uplink transmission slot (or predetermined predetermined uplink transmission slots) in FIG. 1 includes a field for feedback bits, and each downlink transmission slot (or predetermined predetermined downlink transmission slots). Includes a pilot field. Assume that the UE transmits in the field 105 some feedback bits that the BS must interpret as a request to change the antenna weight at the beginning of the next pilot field, namely field 106. The propagation delay causes the BS to receive the feedback bits up to a later delay D than the moment the UE sent the feedback bits. It is clear that the longer the propagation delay (D), the less time the UTRAN to which the BS belongs belongs to acting on the feedback bits and to achieve the requested change of antenna weight. Since the length of the propagation delay is directly proportional to the distance between the UE and the BS, especially in large cells, it is substantially practical to achieve a change in the antenna wage before transmission of the pilot field 106 already proceeds. It may be impossible.

A reliable solution that can allow the UTRAN to always have enough time to process the feedback bits and achieve the requested change is that the feedback bit in the uplink direction where the change is P> 1 as well as at the beginning of the next pilot field. It can be defined that it is effective even at the beginning of the P-th (P: th) pilot field after the reception. However, for the smallest cells (even in large cells if the UE is located in the center of the cell), additional delay in transmission control is completely unnecessary and can seriously adversely affect system stability: CDMA system Their performance is known to depend heavily on transmit power and effective control in phase.

Another obvious solution is to allow the UTRAN to achieve a change in antenna weight at the beginning of the first pilot field after the necessary processing is completed, whether or not the next pilot field is present after the receipt of the feedback bits. To be able. This leaves room for the pilot field to assume that it is the first field where the change is effective under the responsibility of the UE. Although the UE may have a good estimate of the current propagation delay length, leaving an undefined half of the exact time to achieve the change can cause ambiguity and cause serious errors in the power controller. have.

FIELD OF THE INVENTION The present invention generally relates to the field of controlling transmit power and phase in a wireless link between a base transceiver station and a mobile terminal. In particular, the present invention relates to the timing and the transmission factors associated with the achievement of changes.

1 illustrates certain known timing aspects.

2 illustrates certain timing aspects of the method according to the invention.

3 conceptually illustrates a signaling message for signaling a response timing mode.

4 conceptually illustrates a base station in accordance with an embodiment of the present invention.

5 conceptually illustrates a UE according to an embodiment of the present invention.

It is an object of the present invention to provide a method and apparatus for timing the change of antenna weight with a completely deterministic method without unnecessary delay.

The object of the present invention is achieved by defining a number of modes of the base station for responding to feedback bits in uplink slots associated with a change in antenna weight, and by signaling the UE of the mode currently in use.

The method according to the invention comprises the following steps, namely

Selecting a response timing mode from a plurality of predetermined response timing modes;

Informing a terminal of information about the selected response timing mode;

Receiving an initialization from the terminal; And

Characterized in that it comprises the step of responding to the initiation by changing predetermined diversity weights such that the exact moment to achieve a change is determined by the selected response timing mode. .

In addition, the present invention provides the following means:

Means for selecting a response timing mode from a plurality of predetermined response timing modes;

Means for informing a terminal of information about the selected response timing mode;

Means for receiving an initiation from the terminal; And

The apparatus characterized in that it comprises means for responding to the initiation by changing a predetermined diversity weight such that the exact moment to achieve the change is determined by the selected response timing mode.

The length of the propagation delay between the base station and the UE is determined at the very beginning of the communication connection between them, after which it is always monitored to maintain correct synchronization between uplink and downlink slots and frames. A propagation delay to always or regularly infer how much time is required to act on the feedback bits from the UE composing the request to change the antenna weight, either inside the base station or other fixed portion of the network. You can use any known value of. The response timing mode is then selected from a number of predetermined modes. Each mode means a specified delay (in the number of frames) that the base station should take to achieve a change in antenna weight after receiving the corresponding feedback bits from the UE. The selected mode is signaled to the UE to accurately know that the requested change will occur at the point of the downlink transport stream before transmitting any feedback bits that would cause a change in antenna weight.

An advantageous way of performing signaling is to add a new information component to an existing signaling message that characterizes other aspects related to transmit diversity mode. The number of bits requested for the new information component depends on the number of defined response timing modes. If only two modes are defined, the size of the new information component will be a single bit.

The novel features which are considered as features of the invention are described in detail in the appended claims. However, the invention itself, both for its operational structure and its method of operation, together with additional objects and advantages will be best understood from the following description of specific embodiments when read in conjunction with the accompanying drawings.

2 shows the relative timing of uplink and downlink slots at the base station and the UE. Line 201 is a train of downlink transmission slots as the downlink transmission slots are visible to the base station, and line 202 is the same train of downlink transmission slots as the downlink transmission slots are visible to the UE. . Line 203 is a train of uplink transmission slots as uplink transmission slots are visible to the UE, and line 204 is the same train of uplink transmission slots as uplink transmission slots are visible to the base station. The time duration of each slot in both uplink and downlink directions is called a time slot, and its length is 2560 chips. The time slots are numbered, and the synchronization between uplink and downlink is the i-th (i) corresponding to the UE from the moment when the UE receives the start of a predetermined i-th downlink time slot. : th) It is determined that there are 1024 chips up to the moment it starts transmitting in the uplink time slot.

The exemplary slot structure shown in FIG. 2 is referred to as the Dedicated Physical Control CHannel (DPCCH), which is known in both the downlink and uplink directions. The downlink slot includes a Transport Format Combination Indicator (TFCI) field 205, a first data field 206, a transmit power control (TPC) field 207, a second data field 208, and a pilot field 209. Is made of. The data fields are associated with a different channel than the DPCCH. The uplink DPCCH slot consists of a pilot field 210, a TFCI field 211, a feedback information (FBI) field 212, and a TPC field 213. The uplink DPCCH slots shown only in the last two fields in FIG. 2 are associated with the (i-1) th uplink time slots, and the two downlink DPCCH slots shown all of them in FIG. +1) th downlink time slot, respectively.

Feedback bits that allow the UTRAN to potentially change the antenna weight of the base station are located in the FBI field 212 of the uplink DPCCH slot. Arrow 220 indicates the first feedback response timing mode in the UTRAN, whereby the antenna weight is changed at the start of the pilot field in the i th downlink time slot by receiving feedback bits in the (i-1) th uplink time slot. Reference is made. Arrow 221 indicates that the antenna weight is changed at the start of the pilot field in the i + 1 th downlink time slot by receiving feedback bits in the (i-1) th uplink time slot causing the UTRAN to change the antenna weight. Referred to in a second feedback response timing mode in the UTRAN.

Certain exemplary timing considerations may be briefly analyzed based on the slot structure shown in FIG. 2. The number of downlink pilot bits (N _pilot ) in field 209 will be, for example, 4 if the spreading factor SF = 512 is used and 8 if the spreading factor SF = 256 is used. Will be In the worst case, the number N _TPC of uplink TPC bits in field 213 is up one. The time T available for the processing of feedback information in the UTRAN can be calculated from the formula (1) giving time for propagation delay and in units of chips.

Formula (1)

Dividing N _pilot by 2 derives from the fact that pilot bits are Quadrature Phase Shift Keying-modulated, meaning that the number of chips is only one half of the number of bits. N _pilot = 4 and SF = 512 (or equivalently N _pilot = 8, SF = 256) and N _TPC = 1 give T = 768 chips corresponding to approximately 200 ms. It is known that certain alternative settings can be used to determine the number of bits in the field of DPCCH slots; As a more advantageous case, one could have T = 1536 chips or N _pilot = 4, SF = 256 and N _TPC = 2 which would be approximately 400 Hz.

Indeed, it is possible to slightly increase the time margin available for processing and propagation delays by choosing the order of the bits of the FBI field 212 in the most optimal manner. There are two types of bits that can be seen in the FBI field. The so-called D bit is one type that makes the UTRAN deterministic in determining whether the antenna weight should be changed. Another bit type is the S bit, which is related to the Site Selection Diversity TPC (SSDT) and does not include a similar time-critical form. If there is an S bit, there is only one TPC bit in field 213. If there is no S bit, there are two TPC bits. If the D bit is defined to always be transmitted first, the time margin T increases up to 256 chips. However, this addition is not sufficient to ensure that the change in antenna weight is ready before the immediately following downlink pilot field.

The definition of at least two different response timing modes has already been described above. In general, according to the present invention, when feedback bits are received in the jth uplink time slot, k = 1, 2,... , Response timing mode k, where M and at least two positive integers M, are M distinct responses for the base station defined such that a change in antenna weight is achieved at the start of the pilot field of the (j + k) th downlink time slot. There are timing modes. If the numbering of time slots is periodic with period C, then specifying the downlink time slot number corresponding to the kth response timing mode as (j + k) modulus C, where "mod" is a modulus operator Most obvious.

As the most direct case, one may consider the definition of two response timing modes, those shown by arrows 220 and 221 in FIG. 2. When the UTRAN knows the propagation delay between the base station and the UE, to infer the (2-way) propagation delay from the result given by formula (1) and to put a certain requested set of antenna weights into use. It is easy to check whether there is enough remaining time to achieve the requested treatment. Indeed, a first response timing mode (arrow 220) is selected for all base station-UE connections where the propagation delay is below that threshold, and the propagation delay where the propagation delay is equal to or above the threshold. It is most advantageous to store a threshold for the propagation delay such that a second response timing mode (arrow 221) is selected for the connections.

If there are more than two defined response timing modes, it is most advantageous to set up a mapping table where the set of thresholds divides the range of potential propagation delays into storage. Each bin corresponds to a predetermined response timing mode. For each base station-UE connection, it is checked in storing the drop of the propagation delay and the corresponding response timing mode is selected.

Next, the selection signaling of the response timing mode to the UE will be described. It is well known to use a given downlink signaling message to send to the UE certain indicators depicting the transmit diversity mode used at the base station. In the framework of UMTS, the indicator is known as the FB Mode Transmit Diversity Signaling Indicator. Moreover, according to an advantageous embodiment of the invention, an information component is added thereto to indicate the response timing mode selected for the base station. 3 conceptually illustrates a signaling message 301 of another structure beyond the scope of the present invention. Either "0" or "1" corresponding to the first response timing mode (arrow 220 in FIG. 2) or the second response timing mode (arrow 221 in FIG. 2) in the predetermined field 302, respectively. Represents an indicator bit that has a value. Naturally, if several response timing modes are defined, more bits must be assigned to the response timing mode indicator.

4 diagrammatically illustrates a base station that may be used to practice the present invention. Two antennas 401, 402 are connected to a duplexing block 403 that separates the received signals from the transmitted signals. Received signals enter the receiver 404 which converts them into a digital bit stream at baseband frequency. The demultiplexer 405 separates the received payload data from the received control information, the former of which enters the network transmission unit 407 via another multiplexer / demultiplexer 406, the latter of which is specifically delayed. The control portion shown by unit 408 is entered. It associates each communication connection with some measured propagation delay.

The information about the propagation delay is used at block 409 where the corresponding response timing mode is selected. The result of the selection is entered into signaling message configuration block 410, on the one hand, in which the corresponding indicator value is selected and inserted into their signaling message containing the FB mode transport diversity signaling indicator. On the other hand, the response timing mode selection result is connected to the actual antenna weight execution block 411. The information sent to the UE is combined at the multiplexer 412 and converted to radio frequency at the transmitter 413.

5 diagrammatically illustrates a user equipment device that may be used to practice the present invention. Antenna 501 is coupled to duplexing block 502 that separates the received signals from the transmitted signals. The received signals enter a receiver / demultiplexer 503 which converts the signals into a digital bit stream at baseband frequency and performs other known duties of portable terminal receivers. During performing the antenna verification function, payload data enters the downlink user interface 505 which conceptually covers all the individual devices used to provide information to the user. Among the control units of the UE is specifically shown a channel estimation unit 506 which produces a result on which the setting and verification of the antenna weights are based. The last need for antenna weight verification is reported to the signaling message configuration block 508, which sets the FBI bit in accordance with a subsequent uplink signaling message. Uplink user interface block 510 accommodates all components required to convert user input into a transportable form. The transmitter block 511 considers all transmissions.

There is also a connection from the receiver / demultiplexer 503 to the downlink signaling analyzer block 504 that detects the value of the response timing mode indicator in the downlink signaling message and informs the channel guess unit about the mode in use. The channel guessing unit knows in this way the exact moment at which the antenna weight will change and the exact moment at which it can act properly.

In the foregoing, it is assumed that the selection of the response timing mode is performed dynamically for each connection. In some simpler embodiments of the invention, the selection may be based on cell size or processing capacity; For example, a slower response timing mode could always be used in large cells or in cells of base stations with limited processing capacity.

The present invention does not limit the point in the selected slot or frame to be the changing point of the antenna weight. It is advantageous to choose it to be equal to the point of changing the transmit power (ie, the start of the pilot field), but it is also possible to define any other point as the changing point.

Claims (6)

A method for timing the change in diversity weights in a wireless connection between a base station and a terminal, the method comprising: Selecting a response timing mode from a plurality of predetermined response timing modes; Informing the terminal of information about the selected response timing mode; Receiving an initialization from the terminal; And Responding to the initiation by changing a predetermined diversity weight such that the exact moment to achieve the change is determined by the selected response timing mode. The method of claim 1, wherein the step of selecting a response timing mode comprises: Measuring a propagation delay between the base station and the terminal, and -Substeps of the step of mapping the measured propagation delay to a predetermined response timing mode. The method of claim 1, wherein the step of selecting a response timing mode comprises: And selecting a response timing mode based on the cell size of the base station. The method of claim 1, wherein the step of selecting a response timing mode comprises: Selecting a response timing mode based on the processing capacity of the base station. The method of claim 1, wherein the steps of responding to the initiation by receiving an initiation from the terminal and changing a predetermined diversity weight are: Receiving said initiation from said terminal in a predetermined jth (j: th) time slot, and If M represents the period length in a periodic numbering scheme of time slots, then (j + 1) mod Mth time slot or (j + 1) depending on which of the two predefined response timing modes is selected j + 2) substeps of achieving a change in the diversity weight in any one of the modulus Mth time slots. An apparatus for timing changes in diversity weights in a wireless connection between a base station and a terminal, the apparatus comprising: Means for selecting a response timing mode from a plurality of predetermined response timing modes; Means for informing the terminal of information about the selected response timing mode; Means for receiving an initiation from the terminal; And Means for responding to the initiation by changing a predetermined diversity weight such that the exact moment to achieve the change is determined by the selected response timing mode.